Guess I should have said : watch the SSNs and if they sortie from Guam/HI/San Diego, etc.
The subs I referenced are on patrol 24/7/365 and only take to port after being relieved while on station by a replacement. The location of these missile subs are unknown to the Pentagon except for knowing the general area they are patrolling with that area encompassing many thousands of square miles.
There are multiple safeguards built in to ensure they will deliver their payload on the assigned targets even if a first strike against us wipes out every bit of our communications ability.